Trying to get an Ra 32 finish without grinding...
Close
Login to Your Account
Page 1 of 2 12 LastLast
Results 1 to 20 of 31
  1. #1
    Join Date
    Mar 2019
    Country
    UNITED STATES
    State/Province
    Massachusetts
    Posts
    188
    Post Thanks / Like
    Likes (Given)
    76
    Likes (Received)
    98

    Default Trying to get an Ra 32 finish without grinding...

    I have seen some parts lately that call for a Ra32 finish (4140). I cant find any info on improving surface finish with scotch brite pads or emery cloth.

    The parts are not aerospace so I believe the finish is more cosmetic. I do not have a profilometer and I do not know if the customer does either. I know I can make the finish look acceptable from polishing but am not sure if a profilometer would agree with visual inspection.

    Most things I read online have cemet inserts with cnc machines. I have none. Just manual lathes/Brownies. I want to know if anyone has experience trying to polish by hand with good results.

    I have seen some of these automotive parts over the last year have some Ra32 callouts. If its on the O.D. its no big deal as I can have it centerless ground.

    I am not sure if I should be passing on these jobs or if I should have at it. Any advice would be greatly appreciated.

    Most of these parts would be 2nd op on a DV-59. I do have a grinding wheel attachment for a lathe but I have never seen it hooked up. I dont know if I can get it to mount on my DV-59 effectively.

    Thanks in advance.

  2. #2
    Join Date
    Apr 2010
    Location
    Central IL
    Posts
    17
    Post Thanks / Like
    Likes (Given)
    27
    Likes (Received)
    0

    Default

    Using a calculator from this website


    Turning Surface Roughness Calculator

    Shows that’s a 32 finish can be achieved by feeding .0049 per rev with a 1/32” nose radius tool.


    Sent from my iPhone using Tapatalk

  3. #3
    Join Date
    Mar 2005
    Country
    UNITED STATES
    State/Province
    Indiana
    Posts
    4,448
    Post Thanks / Like
    Likes (Given)
    1076
    Likes (Received)
    970

    Default

    Yeah as long as you have your cutting speed up high enough you can pretty easily turn a 32Ra finish. If it's not quite shiny enough give it a quick spin with lightly oiled brown scotch-brite and it will look pretty damn good.

  4. Likes PegroProX440 liked this post
  5. #4
    Join Date
    Mar 2019
    Country
    UNITED STATES
    State/Province
    Massachusetts
    Posts
    188
    Post Thanks / Like
    Likes (Given)
    76
    Likes (Received)
    98

    Default

    Quote Originally Posted by eKretz View Post
    Yeah as long as you have your cutting speed up high enough you can pretty easily turn a 32Ra finish. If it's not quite shiny enough give it a quick spin with lightly oiled brown scotch-brite and it will look pretty damn good.
    I see the 4140/42 comes in Annealed (cuts like 1018), pre heat treated 28/36, and then HT. People have better finishes in the harder materials with cemet (?) inserts. I dont use carbide much or any inserts in my machines. Mostly all HSS, some brazed carbide sticks here and there.

    I like to machine Annealed, Cold Drawn, and use sharpe HSS tools.

    It seems like I should run harder material to get a better finish with a different rake.

    There is a lot of 4130/40/42 work I can get for my machines but I havent run much to get a good idea about it. It seems like just run it a little slower than normal with same tooling should work fine.

    I may have to do a finish pass on my 2nd op with a carbide stick tool. Cranking handles. At least I wont have to send it out for grinding.

  6. #5
    Join Date
    Mar 2005
    Country
    UNITED STATES
    State/Province
    Indiana
    Posts
    4,448
    Post Thanks / Like
    Likes (Given)
    1076
    Likes (Received)
    970

    Default

    If you are running HSS, use the opposite. Slow it way down and take a very light cut with water based coolant. The chips will come off like foil and you'll get a very fine finish. I've gotten an 8 Ra easy that way before. Use a broadnose tool and kick the feed up if time is important. Crucial to keep the depth of cut light for best finish.

    We had a thread about this just recently but I forget where it went. After hearing about this one of the guys here wanted to try it and made a video showing a pretty respectable finish.

    BTW, 4140 is usually sold either annealed or quenched and tempered (aka pre-hard or "HT"). No third option. Annealed is pretty darn soft, HT - or Q&T - is the one that's usually in the high 20's to low 30's Rc. You want it harder than that, you pay someone to HT it.

  7. #6
    Join Date
    Mar 2005
    Location
    Southwestern Ontario, Canada
    Posts
    131
    Post Thanks / Like
    Likes (Given)
    9
    Likes (Received)
    6

    Default

    Surface finish is nothing to do with how shiny it is. It has to do with nose radius vs feed rate, and how high the scallops left behind are. Which is average roughness. One other poster up top is right with the finish calculator.

  8. #7
    Join Date
    Mar 2019
    Country
    UNITED STATES
    State/Province
    Massachusetts
    Posts
    188
    Post Thanks / Like
    Likes (Given)
    76
    Likes (Received)
    98

    Default

    Well I do not have the luxury of a constant feed rate due to cranking handles. No water based coolant either.

    I get the nose radius and feed rates situation. This part doesnt make sense for me to take on it looks like. Too many problems could arise.

    Thanks for the heads up guys

  9. #8
    Join Date
    Feb 2018
    Country
    UNITED STATES
    State/Province
    Texas
    Posts
    87
    Post Thanks / Like

    Default

    Quote Originally Posted by DanASM View Post
    I see the 4140/42 comes in Annealed (cuts like 1018), pre heat treated 28/36, and then HT. People have better finishes in the harder materials with cemet (?) inserts. I dont use carbide much or any inserts in my machines. Mostly all HSS, some brazed carbide sticks here and there.

    I like to machine Annealed, Cold Drawn, and use sharpe HSS tools.

    It seems like I should run harder material to get a better finish with a different rake.

    There is a lot of 4130/40/42 work I can get for my machines but I havent run much to get a good idea about it. It seems like just run it a little slower than normal with same tooling should work fine.

    I may have to do a finish pass on my 2nd op with a carbide stick tool. Cranking handles. At least I wont have to send it out for grinding.
    If you can get a lot of work why not get a proper Gauge, then you will know for shure.

    https://www.mscdirect.com/browse/tn/...navid=12107998

  10. #9
    Join Date
    Apr 2018
    Country
    UNITED STATES MINOR OUTLYING ISLANDS
    Posts
    3,901
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1761

    Default

    Quote Originally Posted by mc3608 View Post
    If you can get a lot of work why not get a proper Gauge, then you will know for shure.

    https://www.mscdirect.com/browse/tn/...navid=12107998
    "MSCdirect.com is currently not available for your use."

    So I could be mistaken about what you linked to .... but there is a low-cost method. You can buy nickel-plated roughness sample plates that have a variety of surface finishes. They used to be pretty cheap. It's not a $4,000 gage but better than guessing.

    You can use your fingernail to compare, but for max sensitivity use your front teeth, like a bunny. Your teeth are more sensitive than your fingernails.

    Seriously

    Agree that surface finish and shininess are not the same, what I found was that you tailor what you do to the customer. The ones that mean "shiny" when they put a small number on the print get shiny, and the ones that know what they are doing get what they put on the print. Sometimes you have to interpret these things ...

  11. Likes eKretz liked this post
  12. #10
    Join Date
    Mar 2005
    Country
    UNITED STATES
    State/Province
    Indiana
    Posts
    4,448
    Post Thanks / Like
    Likes (Given)
    1076
    Likes (Received)
    970

    Default

    While it is true that the calculators for nose radius and feed rate are very useful, they don't always tell the whole story. You still need to be making it "shiny" or you're likely producing a torn finish. This does show up on the profilometer as a significant difference in Ra. For steel, "shiny" is also significantly more resistant to rusting in my experience.

  13. #11
    Join Date
    Mar 2019
    Country
    UNITED STATES
    State/Province
    Massachusetts
    Posts
    188
    Post Thanks / Like
    Likes (Given)
    76
    Likes (Received)
    98

    Default

    Quote Originally Posted by EmanuelGoldstein View Post
    "MSCdirect.com is currently not available for your use."

    So I could be mistaken about what you linked to .... but there is a low-cost method. You can buy nickel-plated roughness sample plates that have a variety of surface finishes. They used to be pretty cheap. It's not a $4,000 gage but better than guessing.

    You can use your fingernail to compare, but for max sensitivity use your front teeth, like a bunny. Your teeth are more sensitive than your fingernails.

    Seriously

    Agree that surface finish and shininess are not the same, what I found was that you tailor what you do to the customer. The ones that mean "shiny" when they put a small number on the print get shiny, and the ones that know what they are doing get what they put on the print. Sometimes you have to interpret these things ...
    I have a roughness sample plate. It would still be up to me to determine by vision if it is good or not. I have seen profilometers contradict what the eye says is good. I do not want these issues to come up so I will not put myself in that situation.

    I figured I could do a finish pass and skim .005 with a carbide brazed stick. Then polish with scotch brite or emery cloth.

    If the finish still isnt good enough at that point it would not be profitable. It may take too long to do the skim pass and polish just in cycle time to make the part affordable anyway. Someone with a cnc lathe would bang this out easily with no headaches.

  14. #12
    Join Date
    May 2009
    Location
    Canandaigua, NY, USA
    Posts
    2,936
    Post Thanks / Like
    Likes (Given)
    146
    Likes (Received)
    1327

    Default

    A 32 finish isn't all that great. If this is turning, try a shear tool. That will work on the worst steel and look like it's ground.

  15. #13
    Join Date
    Mar 2019
    Country
    UNITED STATES
    State/Province
    Massachusetts
    Posts
    188
    Post Thanks / Like
    Likes (Given)
    76
    Likes (Received)
    98

    Default

    Quote Originally Posted by mc3608 View Post
    If you can get a lot of work why not get a proper Gauge, then you will know for shure.

    https://www.mscdirect.com/browse/tn/...navid=12107998
    The work is 4130/40/42 material. They do not always ask for a surface finish requirements. Hence no need for $2k-$5k profilometer

  16. #14
    Join Date
    Oct 2005
    Country
    UNITED STATES
    State/Province
    Pennsylvania
    Posts
    16,666
    Post Thanks / Like

    Default

    It would be nice if you could swing down a Supfina attachment, maybe from the back of the cross slide ?

    Drop it on there and let it polish for 15 seconds or so as the spindle rotates slowly, flood coolant.

  17. #15
    Join Date
    Mar 2019
    Country
    UNITED STATES
    State/Province
    Massachusetts
    Posts
    188
    Post Thanks / Like
    Likes (Given)
    76
    Likes (Received)
    98

    Default

    Quote Originally Posted by digger doug View Post
    It would be nice if you could swing down a Supfina attachment, maybe from the back of the cross slide ?

    Drop it on there and let it polish for 15 seconds or so as the spindle rotates slowly, flood coolant.
    I do have a grinding wheel attachment for lathes. I pulled it out 6 months ago and didnt see how I could mount it. If I remember correctly I need to make a mounting plate for it. I will have to pull it out again and take a look at it. It seems like I can get some good use out of it if I can get it mounted right.

    Where there is a will there is a way.

    This part has 2 center drill marks on the ends for 2nd op I imagine. Its a 4.5" long part. Probably chucked up like that for the grinding/finish pass. It says the centering holes are optional but were put on the print years ago for a reason. Someone probably made this part the same way I am quoting it.

  18. #16
    Join Date
    Oct 2005
    Country
    UNITED STATES
    State/Province
    Pennsylvania
    Posts
    16,666
    Post Thanks / Like

    Default

    Quote Originally Posted by DanASM View Post
    I do have a grinding wheel attachment for lathes. I pulled it out 6 months ago and didnt see how I could mount it. If I remember correctly I need to make a mounting plate for it. I will have to pull it out again and take a look at it. It seems like I can get some good use out of it if I can get it mounted right.

    Where there is a will there is a way.
    I did NOT say "Grinding Wheel".

    I said "Supfina".

    Google is your friend.

    FWIW they appear to be local to you (somewhat)

  19. #17
    Join Date
    Mar 2019
    Country
    UNITED STATES
    State/Province
    Massachusetts
    Posts
    188
    Post Thanks / Like
    Likes (Given)
    76
    Likes (Received)
    98

    Default

    Quote Originally Posted by digger doug View Post
    I did NOT say "Grinding Wheel".

    I said "Supfina".

    Google is your friend.

    FWIW they appear to be local to you (somewhat)
    I know you did not say "grinding wheel".
    I said Grinding wheel.

    Thanks for the help though

  20. #18
    Join Date
    Sep 2002
    Location
    People's Republic
    Posts
    3,934
    Post Thanks / Like
    Likes (Given)
    350
    Likes (Received)
    2483

    Default

    I think you may be overthinking this

    A 32 finish is a nice finish, but does not require grinding. I personally would think a 16 would.

    If you are turning with a decent nose radius and a fine feed, providing your machine is not imparting any glitches[like if you were using the compound manually with no finesse, you should meet a 32 with at most a quick hit with fine emer

    I mean a 63 is a standard machined finish

  21. #19
    Join Date
    Jun 2006
    Location
    Hawthorne, CA USA
    Posts
    199
    Post Thanks / Like
    Likes (Given)
    41
    Likes (Received)
    67

    Default

    Just a few thoughts.
    Is the drawing per ASME / ANSI Y14.5? If so the Surface Texture (not surface finish) is per ASME B46.1
    This can be a complicated subject if you read the whole spec.
    Are their and modifiers in the callout MAX? LAY? TURN,GRIND,HONE? Sample length? Sub surface imperfections not allowed?

    32Ra is not very specific, which is good for manufacturing flexibility. I would compare with a tactile specimen using a #2 pencil.

  22. #20
    Join Date
    Apr 2018
    Country
    UNITED STATES MINOR OUTLYING ISLANDS
    Posts
    3,901
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1761

    Default

    Quote Originally Posted by DanASM View Post
    I have a roughness sample plate. It would still be up to me to determine by vision if it is good or not.
    You're not supposed to look at it, you run your fingernail across the surfaces and compare. For exacting work, you use your teeth.

  23. Likes eKretz liked this post

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •